US lawmakers have been urged to take action to prevent future shortages by enacting the Drug Shortage Prevention Bill. Photograph: David Sillitoe for the Guardian

Critical shortages of two cancer drugs that have threatened the lives and care of thousands of patients will be eased in weeks, at least temporarily, after federal drug regulators approved new suppliers.

The move by the Food and Drug Administration has brought relief to some cancer patients, including children with acute lymphoblastic leukaemia (ALL), whose treatment relies on a preservative-free version of methotrexate. The version with preservatives can be toxic or cause paralysis in children and other patients who need the drug in very high doses or via injection.

On Tuesday, the FDA said it had approved new suppliers for preservative-free methotrexate and a replacement for Doxil, a drug used to treat ovarian cancer, AIDS-related Kaposi's sarcoma and multiple myeloma, which had not been available to new patients for months.

The FDA also approved the release of a batch of methotrexate produced before the manufacturer closed its factory over serious quality problems.

Doctors and paediatricians welcomed the news as a "major step forward" but called for more to be done on other drug shortages.

Across the US, there are currently 283 separate drugs in short supply or unavailable.

Temporary shortages of methotrexate began in 2008 but when manufacturer Ben Venue Laboratories closed its factory in Bedford, Ohio, it sparked a crisis, with predictions that patients would begin missing treatments this month.

Dr Len Lichtenfeld, the deputy chief medical officer of the American Cancer Society, called the FDA move a "major step forward" to address what he described as the "daily nightmare" faced by patients and their families.

At a press conference held by the FDA, Lichtenfeld said that some patients had postponed their treatment and others have been forced to turn to the grey markets for drugs.

Dr Peter Adamson, chairman of the Children's Oncology Group, a network of 200-plus North American hospitals treating children with cancer, said: "There are potential future crises waiting to happen."

He urged lawmakers to take action to prevent future shortages by enacting the Drug Shortage Prevention Bill, aimed at requiring the FDA to take action to prevent drug shortages before they begin impacting patients.

Adamson said: "If we can induce a remission for children with cancer in four weeks then I would challenge my colleagues in Washington to enact legislation in four weeks' time."

FDA commissioner Margaret Hamburg told the Associated Press: "We have made real progress … We believe that [suppliers] will be able to meet the demands of patients in the US market for the two drugs indefinitely. It's a huge relief for us."

Hamburg told a press conference that 11 full-time staff were working "night and day" on the issue. They had been able to prevent drug shortages, mainly due to a sixfold increase in manufacturers voluntarily notifying the FDA when they anticipate shortages, Hamburg said.

She said they had prevented 195 drug shortages in 2011, mostly late that year, after President Obama issued an executive order which required drug companies to alert the FDA when potential hitches threaten supply. Between that order and this week, a further 114 drug shortages had been prevented.

The FDA temporarily allowed the importation of Lipodox, an alternative to Doxil, which is made by Sun Pharma Global FZE, from India. The factory and production line for Lipodox has been inspected.

Hospira, another pharmaceutical company, will provide 31,000 vials of methotrexate from its plant in Australia, enough to last the US a month.

A similar quantity would be also be supplied next week, and 55,000 vials in mid-March, according to Hospira. A spokesman told a press conference that it was able to make the additional vials available by "scouring the globe" for FDA-approved active ingredient being used by other companies that make the medicine.

In mid-March, the FDA will begin shipping medication from another manufacturer, APP Pharmaceuticals. The company is to begin making a preservative-free version of methotrexate in addition to its current drug that includes preservatives.

Drug shortages have increased dramatically in the US over the past six years, particularly for generic injected drugs. They are difficult to make and provide little profit for manufacturers.

At least 15 deaths have been blamed on the shortages.

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